How should drivers handle rain after a dry spell?

Q: What are the most dangerous stretches of highway locally after rainfall?

A: We’re taught in driver’s ed that the roads are most dangerous when rain hits dry pavement, as it has in the past couple days.

But State Trooper Chris Webb says that drivers can’t really prevent danger by avoiding certain roads. Rather, it’s drivers’ behavior that can make a dangerous road more or less safe in rainy conditions.

Says Webb:

With thousands of miles of roadways in the Puget Sound area, it would be impossible to be specific on which highways are more dangerous after rainfall. Most collisions are caused by drivers and not the engineering of roadways. Little things such as increased following distance, control of speed and having a well equipped vehicle (all season tires with adequate tread depth, good brakes and suspension) will go a long way in preventing collisions. Most of all, be patient; when we get our first significant rain, after a dry summer, it is almost guaranteed that traffic volume will be challenging.

So basically, be smart out there.

What is it about the first big rainfall after a dry spell that makes roads more treacherous? UW professor of atmospheric sciences Cliff Mass explains it briefly in a 2009 blog post:

During the dry period oil, dust and other debris collect on roadways and the addition of water produces a slippery emulsion. After a few days of rain, it washes off. The other issue is that people are used to dry-road driving and driving habits (like taking that corner slower) are slow to change.